[PATCH] D27686: Add llvm::StringLiteral

[Zachary Turner via llvm-commits]

Appears to work fine, submitted in r290188.

On Mon, Dec 19, 2016 at 8:41 PM David Blaikie <dblaikie at gmail.com> wrote:

Ping on Eli's feedback - it sounds plausible to me.

On Tue, Dec 13, 2016 at 10:38 AM Eli Friedman via Phabricator via
llvm-commits <llvm-commits at lists.llvm.org> wrote:

efriedma added inline comments.


================
Comment at: include/llvm/ADT/StringRef.h:90
-        assert((data || length == 0) &&
-        "StringRef cannot be built from a NULL argument with non-null
length");
-      }
----------------
zturner wrote:
> efriedma wrote:
> > mehdi_amini wrote:
> > > Too bad we're losing the assert, but I see why. An alternative is
another (possibly protected) ctor that would be constexpr and used by
`StringLiteral`
> > Stupid trick to save the assert:
> >
> >     /*implicit*/ constexpr StringRef(const char *data, long length)
> >         : Data(data), Length((data || length == 0) ? length : (assert(0
&& "Bad StringRef"), 0)) { }
> >
> >
> Won't this still complain that `assert` is not a constant expression and
thus can't be used in a `constexpr` function?
No... formally, [expr.const] in the C++11 standard says that when checking
whether an expression is a constant expression, "conditional operations
that are not evaluated are not considered".  In practice, this means you'll
get an error at compile time only if the condition is false, which is
exactly the behavior you want.

I actually screwed up the implementation slightly; it's not a no-op if
assertions are turned off, but that's easy to fix:

    /*implicit*/ constexpr StringRef(const char *data, long length)
        : Data(data), Length((data || length == 0) ? length : (assert(0 &&
"Bad StringRef"), length)) { }


Repository:
  rL LLVM

https://reviews.llvm.org/D27686



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